1. Field of the Invention
The present invention relates to a cleaning apparatus and more particularly, to a photomask cleaner, which cleans the photomask automatically and, which holds the photomask positively for cleaning and will not release the photomask in case of a power failure during the cleaning operation.
2. Description of the Related Art
As the world entered the 21st century, the digital era begins to change human life. Digitalized high-tech products such as computer, digital TV, digital audio and video apparatus, building control system and many other digitalized products have been continuously developed to bring convenience to people. These high-tech products commonly use an IC chip for operation control. Therefore, some people asserted that IC chip is a mother of the industry. An IC chip is a miniaturized electronic circuit consisting of semiconductor devices and passive components. IC chips are fabricated with a photomask in clean environment in a layer process, which includes imaging, deposition and etching process steps. The plant and equipments for the fabrication of IC chips or wafers are quite expensive. The yield rate determines the profitability of a wafer foundry. Therefore, every semiconductor supplier is trying hard to improve their yield rate.
Contamination of photomask is an important factor that affects the yield rate of the fabrication of wafers. If particles appear on a photomask, the use of this contaminated photomask in semiconductor lithography will cause wafer defects. In order to keep a photomask clean, a pellicle will be used above the photomask to protect the photomask against particles. The pellicle is supported on a frame and spaced above the photomask at a distance to collect particles.
Before delivery to the client or the performance of a lithography process, the photomask must be scanned to check the pattern. In case of a defect, the pellicle must be removed from the photomask, and then the photomask must be cleaned in an acid trough. During the cleaning operation, SPM solution is used to remove big organic molecules, and SCI solutions is used to remove small organic molecules and particles. Thereafter, deionized water is used to remove residual cleaning solution from the photomask. After cleaning, a new pellicle is placed on the well-cleaned photomask. Because a pellicle is an expensive device. Removing a contaminated pellicle from a photomask and replacing a photomask with a new pellicle greatly increases the photomask using cost. Further, the glue used in a photomask is generally prepared from esters (RCOOR)x, for example, polyacrylate. When a photomask is dipped in SPM solution, (RCOOR)x is dehydrated into gel-like (RCOOR)x that floats on water but not soluble in water. Dehydrolysis of (RCOOR)x may cause defects on the pattern of the photomask. Therefore, a photomask must be thrown away when cleaned three times. Because a photomask is quite expensive and cannot be used repeatedly for more many times, the cost of photomask utilization is high.
Therefore, it is desirable to provide a way that solve the aforesaid problem.